A Comparison of Treatment, Chemistry and in-Vitro Bioassay Responses During the Digestion of Combined Sludges

The proposed work is intended to extend our process knowledge related to co-treatment of municipal primary sludge (PS) and thickened waste activated sludge (TWAS) using a pilot scale sidestream anaerobic membrane bioreactor (AnMBR) compared to a conventional flow-through anaerobic digester (AD) under mesophilic and psychrophilic conditions (only mesophilic phase is presented here). The membrane performance with respect to critical and sustained flux, under various total solids (TS) loadings were investigated and preliminary results indicate a 30 to 50% reduction in the critical flux when compared to reduced TS loadings with TWAS alone. The membrane cleaning strategies of using abrasion, water flush, alkali followed by acid clean were effective at recovering lost flux. A permeation relaxation mode of operation during the permeation cycle (5 minutes permeation followed by 1 minute relaxation) was implemented and found to be effective at recovering the flux decline during permeation. The resulting treated sludge or biosolids quality will be compared for the concentration of selected EDCs along with the whole sludge extracts and permeate estrogenic and androgenic response using yeast bioassay screens (YES and YAS). Preliminary results indicate that the average relative estrogenic response increases following anaerobic digestion (AD) and in the permeate of the anaerobic membrane bioreactor (AnMBR).